The present invention relates to a gradient magnetic field generating coil assembly of a magnetic resonance (MR) imaging apparatus, and more particularly to a gradient magnetic field-generating coil assembly of an MR imaging apparatus having a function of extracting information about the position of a tomographic image and a construction effective to reduce noise.
In a conventional gradient magnetic field-generating coil assembly of an MR imaging apparatus, a core having substantially the same axial length as a magnet for generation of a static magnetic field and made of synthetic resin (especially FRP) is provided, a lap winding of coils corresponding to X, Y and Z axes, respectively, is wound on the core and the coils are held by a coil fixing plate made of metal or synthetic resin. When the gradient magnetic field-generating coil assembly having the above construction is driven by a constant-current driven power amplifier, a strong electromagnetic force is exerted on the coils instantaneously to cause them to vibrate, the vibration is transmitted to the cylindrical core via the coil fixing part to generate noise by hitting the core, and at the same time the transmitted vibration causes a natural vibration of an annulus of the core so as to generate resonant sound, leading to simultaneous occurrence of a cavity resonance inside the cylinder.
A prior art apparatus contrived to solve the above problems is disclosed in Japanese Patent Application No. JP-A-58-89147. In the apparatus disclosed in this literature, a cylindrical core is formed with many perforations to take the form of a basket. With this construction, the inside and outside of the winding join together spatially through the perforations, with the result that a sound wave prevailing in the outside passes through the perforations to interfere with a 180.degree. dephased sound wave prevailing in the inside to thereby reduce developing noise.
However, because of the structure of the basket-like cylindrical core, it is very difficult to design a core of this type which can have sufficient mechanical strength to prevent deformation of the core due to the weight of the coils and the resulting electromagnetic force, and which can maintain sufficient mechanical strength to suppress vibratory displacement of the coils. In addition, employed for making the basket-like cylindrical core is either a method of boring a cylindrical core or a method of putting together short cylindrical cores or plates and assembling and bonding them. Any of these methods require much labor and much labor time and are very difficult to actually practice.